The moisture behind the mystery
What is the dew point—and why does it matter?
The dew point is the temperature at which moisture in the air starts turning into liquid water.
Think of a cold drink.
The droplets on the outside come from the surrounding air—not from inside the glass. The glass cools the air touching it to its dew point, and condensation forms.
The same thing happens inside buildings.
When moist air touches a wall, roof or pipe at or below its dew point, condensation forms—even without a rain leak.
This principle applies in all 50 states.
In Chicago, Philadelphia, Boston, New York, Minneapolis and other places with cold winters, parts of roofs and walls become cold. In Florida, Houston, New Orleans, Atlanta and other warm, humid areas, air conditioning creates cold surfaces inside buildings.
Many places experience both conditions at different times of year. Wherever moist air meets a surface at or below its dew point, condensation forms.
Hidden surfaces. Hidden moisture.
If those surfaces are hidden, the moisture is hidden too. Repeated condensation without enough drying leaves materials wet and creates conditions for mold and wood decay.
The question is simple: Where does moisture meet a cold surface—and how does that area dry?
Explore what this means for your building: